1. Field
Embodiments of the present invention relate to prosthesis of an anterior spinal column, a prosthesis-guiding instrument and a method for installation thereof for use in the treatment of cervical, thoracic, and lumbar spinal segments.
2. Related Art
As described in U.S. patent application US2009/0149955, a spinal prosthesis is known in the form of a cylinder with a perforated wall and prostheses of intervertebral discs attached thereto made of spring silicone rubber in the shape of balloons. Anchoring of the cylinder in the damaged vertebra is provided by means of an entrapment of an elongate lug of the cylinder within a slot of a plate retained by screws within a recess of the damaged vertebra. Springs of resilient beads are attached to the natural vertebrae, superior and inferior to the damaged vertebra, by fixing plates provided with flanges that are fixed by screws to those vertebrae. Where adjoining vertebrae are damaged, two or more prosthetic cylinders for anchoring to a single vertebra are used with interconnecting resilient beads. The inconvenience of this solution is its complex structure and the necessity of boring into vertebral bone during installation of the prosthesis and fixing it with additional screws.
U.S. patent application US2006/064168 discloses a prosthesis for a partial replacement of a vertebral body, which has an upper contact plate for connection to an upper vertebral body, a lower contact plate for connection to a lower vertebral body, and a bridging part which connects the upper and lower contact plates to each other and bridges at least one vertebral body located between the upper and lower vertebral bodies. The bridging part is accommodated in a recess in the vertebral body. To be secured in said recess, the prosthesis has lateral anchoring projections, which penetrate into the bone substance, located on both sides of the bridging part. Its cross section narrows toward the rear preferably in a trapezoid shape. The inconvenience of this solution is the complex structure of the prosthesis and necessity of accommodating the bony recess to the bridging part to reinforce the support of the vertebral body.
A prosthesis for the replacement of all vertebral elements such as the vertebral body, the pedicles with the joint facets and the lamina, is disclosed in the European patent application EP1188424. This prosthesis has interconnection capability to a posterior fusion system by means of special screws. The prosthesis consists of a front part, which in a section is in an octagonal shape and screws that can connect the prosthesis to a posterior fixation pedicle screw system and thus create a complete construction which replaces a whole dislocated vertebral unit. The inconvenience of this solution is the necessity of cooperation with an additional posterior spinal stabilization by a posterior fusion system and the complicated two-stage surgical operation—first, using the posterior, and then using an anterior-lateral approach.
A prosthesis which has a telescopic perforated cylinder is disclosed in the European patent application EP 0968692 The cylinder consists of two parts and an intersected shield, connected by screws. The telescopic construction allows regulating the length of the prosthesis depending on the distance between the neighboring vertebrae. The prosthesis is situated in a definite position by two external screws fixed in the cylinder's hole. The cylinder is provided with teeth and other anchoring elements preventing sliding of the prosthesis and a decrease of its height during implantation. The inconvenience of this solution is the multi-element construction of the prosthesis. Bearing surfaces of the prosthesis are small, which decreases its load bearing capacity. The round shape of cylinders is not accommodated to the anatomy of the spine. For a proper placement of the prosthesis it is necessary to use an external element in the form of the above mentioned screws.
Another inconvenience of the solutions described above is the long duration of surgical implantation of the prosthesis between adjacent vertebrae, the necessity of its fastening with additional screws, and in some cases the necessity of additional stabilization, which complicates the surgery and prolongs implantation time.
A monorail system, which improves the use of the procedure of a spinal fusion, and a method for preparation of the intervertebral space and introduction of the implant are known from the patent application US 2007/0270873. The system consists of an instrument for distraction of the intervertebral space, preferably in the form of a rod having a rail, a chisel provided with a canal cooperating with the rail and an implant provided with a canal cooperating with the rail. The instrument for distraction, comprising a sliding section defined by the rail, cooperates with other instruments used for preparation of the intervertebral space and may act as an instrument for inserting the implant into the intervertebral space. The canals of the instrument and the implant are connected with the rail during guiding and controlling their insertion into the disc space. The inconvenience of this solution is a lack of the possibility of positioning and anchoring the instrument during insertion of the implant into the intervertebral space. Moreover, there is a possibility that the instrument may slide and harm sensitive tissues.
A method of installation of an expandable prosthesis for support of the anterior spinal column is known from instructions for an implant by LfC Sp. z.o.o. The method comprises resectioning vertebral body/bodies to enable secure, axial installation of a prosthesis and then measuring the resected space height. Next, this method comprises accurately selecting a prosthesis with regard to biomechanical and dimensional aspects corresponding to the size of the resected space, and filling the selected prosthesis with an autogenous bone graft or another material enabling bone fusion. Then this method includes inserting the prosthesis into surgically prepared space with a “spacer grasper” in a way enabling a free approach to a blocking screw, paying special attention to proper placement of external resistance rings with respect to a bearing surface of the vertebral body, so as not to irritate the spinal cord. The prosthesis is then extended with a “spacer dilator” to a required height, performing a desired distraction, and securing placement of the prosthesis between vertebral bodies, followed by complementing the inside of the prosthesis with an autogenous bone graft or anther material enabling bone fusion through special slots in sleeves. Next, the method may comprise screwing down the blocking screw into a transverse notch of an inner sleeve so as to stabilize and securely block the mutual position of both sleeves of the spacer, followed by releasing the instrument and withdrawing it from the surgical field.
A method of performance of vertebral body replacement surgery is known from instructions for the Expandable Corpectomy Device (ECD) implant of SYNTHES INC. The method comprises performing corpectomy and cleaning vertebral endplates, performing spinal segment distraction for setting the anatomic height of intervertebral space, selecting an implant size, and then connecting the implant to a holding-distraction instrument by placing the implant's teeth in notches of the implant. Next, this method comprises placing the prosthesis in a resected part of the spine and aligning it in a sagittal and frontal plane, the optimal arrangement of the implant being the center of the vertebral endplate. To provide bone fusion, some space around vertebral endplates has to be provided. Then the implant may be extended in situ with the holding-distraction instrument by rotating a handle of the instrument until a desired height of the implant is reached and the prosthesis anchors in vertebral endplates. The final steps of the method include releasing the implant from the instrument, and filling the space around the implant, especially its anterior part, with a bone graft or bone substitute.
The inconveniences of the above mentioned methods arise from their complexity and duration of surgery.